AF3 project creation/import etc fails if the AF3-Project-Directory was delete on the file system

Observed Behavior

If the AF3-Project-Directory were deleted on the file system, and then AF3 were launched, no new Projects can be created/imported etc.

Technical Explanation

The AF3-Project-Directory is the project visible to eclipse. By deleting the folder, the metadata of the project remains. As a consequence, the AF3/Eclipse logic is utterly confused.

Testing

FOR THE FIRST THREE STEPS, USE THE MASTER BRANCH!!!

1. Start AF3 with a fresh runtime workspace and load the ACC example. Close AF3.
2. Delete the AF3-Project-Directory from the runtime workspace.
3. Start AF3 and notice the warning and the exception when trying to create a new project.
   SWITCH TO THE BRANCH
4. Start AF3 and create a Project. There shall be no warning or exception.

(from redmine: issue id 4042, created on 2020-07-02, closed on 2020-07-03)